102 



SCIENTIFIC NEWS. 



[Aug. 3, 1888. 



the liquid reassumes its gaseous form, precisely as heat 

 disappears when ice loses its solid form and becomes 

 water. 



Bulk for bulk, we can get the same effect from 42 

 cubic feet of ether as from 100 cubic feet of air. But 

 ether is inflammable and expensive, and we can get the 

 same effect with only 23 cubic feet of anhydrous 

 ammonia. Ordinary aqua ammonice or " spirits of harts- 

 horn " is a solution of ammonia gas in water. The 

 greediness with which water will dissolve ammonia is 

 used in another form of refrigeration which is not strictly 

 mechanical, and which we must leave for another 

 occasion. The ammonia compression system is the same 

 in principle as the compressed air method, but the 

 ammonia gas itself is not liberated in the chill rooms, but 

 circulates in iron pipes. 



One of the most perfect systems of ammonia refrigera- 

 tion is that oi the De La Vergne Co. of New York, and 

 in the hands of Messrs. L. Sterne and Co., of West- 

 minster and Glasgow, it is being most successfully 

 introduced into this country. Few passengers in 

 Gracechurch-street during this uncertain and muggy 

 weather, know that within a few feet of the pavement 

 there is an unvarying temperature of about 22 Fahren- 

 heit, in which thousands of carcases of mutton are stored 

 in chambers, tons of Russian hares and game, waiting 

 until they are " in season," or to be consumed by the 

 owners out of season. The meat seems as hard as stone, 

 and a pair of fowls knocked together ring like flints. 

 The air is so dry that it is difficult to believe that the 

 temperature is ten degrees below freezing point. 



Electric light glistens on the hoar frost which lies thick 

 upon the pipes that run along the ceilings ; they are pro- 

 vided with cast-iron discs, which afford a large surface 

 for the absorption of heat. In these pipes the ammonia 

 gas is passing. On leaving the chill-rooms the ammonia, 

 in the form of a gas at about 15 to 18 lbs. pressure, 

 enters at the bottom of a compressing pump which 

 is worked by a Corliss engine. With the gas, mineral 

 oil is forced in. This seals the valve and stuffing-box 

 of the piston rod, and some of it is carried up 

 with the piston, sealing the valves with which it 

 is provided, and lubricating the cylinder at the 

 same time. At the end of the up stroke, not only is all 

 the gas expelled, but some of the oil as well. The 

 ammonia is now at a pressure of 150 lbs. The pure gas 

 has so much better a result than a mixture of ammonia 

 and water, that the cooling is not effected by a shower of 

 water as in the air compressing system, but it is led 

 through long coils of pipes, shown in the illustration 

 on the floor above the engine. A stream of water flows 

 over these pipes, and the warm gas entering at the 

 bottom, gradually exchanges its heat with the water, which 

 runs off below at about the temperature of the warm am- 

 monia, while the gas which reaches the top is at the 

 temperature of the cold water. In the language of the 

 caloric theory it would be said that the warm water 

 leaving the cooler, carries off the caloric which has been 

 squeezed out of the ammonia by the pump. Very little 

 of the gas reaches the top, for the cooling combined with 

 the pressure liquefies it, and as fast as it becomes con- 

 densed, it runs off by the pipes shown at the right-hand 

 side of the cooler. It now is stored in a tank as cold liquid 

 ammonia, the oil having been separated by a system of 

 tanks which we have no space to describe. From the 

 tank, the liquid is led to a row of valves provided with 

 very small wedge-shaped openings, by which very 



accurate adjustment can be made. These valves open 

 into the circulating pipes which run through the chill- 

 rooms. In the cooling coils, the ammonia parted not only 

 with the heat generated by the compression in the pump . 

 but with the latent heat which would be necessary to 

 boil it from the liquid into the gaseous state. As it 

 rushes through the valve into the circulating pipes, and 

 resumes the form of gas, the latent heat is abstracted 

 from the pipes, and these becoming intensely cold, chill 

 the surrounding air. In addition to the chill-rooms, the 

 same machinery is used for making ice. For this purpose 

 the ammonia in expanding, circulates in a set of pipes 

 like those of the cooler shown in the illustration above 

 the engine. A stream of strong brine flows over them, 

 and becomes chilled to a temperature of about 23 . It is 

 then pumped into a large tank, in which are placed a 

 number of cans containing distilled water. This water 

 being not only pure, but also free from air, freezes into 

 blocks of ice as clear as crystal; and solid all through. 

 These are so much below freezing point when removed 

 from the cans, that if two are left touching they will 

 instantly freeze hard together. 



BIRDS' NEST, OR ELEPHANT 

 ISLANDS. 



Part I. of Vol. XXI. of the Records of the Geological Sur- 

 vey of India furnishes some interesting information con- 

 cerning this remarkable group called by the Burmans 

 Ye-eigent-thaik (lit., sea-birds' nests) at the southern 

 extremity of Burma. It is a small group of six marble 

 rocks, the highest and largest of which, 1,000 feet in 

 height and above one mile in length, is oval shaped, and 

 rises very abruptly out of a depth of only five fathoms. 

 The sides are partly clothed with vegetation wherever a 

 break in the limestone has left a cleft in which moisture 

 and dust can lodge. Conspicuous is a species of tree- 

 fern which grows at any angle, but only above a height of 

 200 feet from the water. The face of the rocks is reddish, 

 and where cliffs exist most beautiful stalactites are 

 in course of formation. But the great feature of the group 

 are the birds' nest caverns, which, as a rule, open into 

 the sea, the entrance being below high-water mark. At 

 half-tide a tunnel opens under a wall of rock at the head 

 of a deep cove in the big island ; this tunnel has a roof- 

 covering with large stalactitic knobs. Passing through 

 this, one emerges into another circular basin with per- 

 pendicular sides, which gives the impression of volcanic 

 action. Great caverns opening into circular basins exist 

 in other parts of the island, and Commander Alfred Car- 

 penter, R.N., who writes the account, states that the 

 impression gradually forces itself on one that these 

 circular basins were at one time the floors of huge 

 caverns, and that, in days gone by, the islands were far 

 higher with cavern piled on cavern, and that the work 

 of disintegration by moisture is slowly going on pulling 

 down these marble monuments of the past. 



Progress of the Asbestos Trade. — The output of 

 asbestos at the Canadian mines has risen from 300 tons 

 in 1879, to 3,458 tons in 1887. It is now considered to 

 yield the best and safest returns of any kind of mineral. 

 A somewhat curious fact is that in China asbestos ranks 

 among the medicines for inward use, being regarded as a 

 tonic. 



